In August, a few days after Solomon Thomas’ NFL debut in the preseason opener at Kansas City, 49ers general manager John Lynch said plenty of people in his circle had noticed the rookie defensive lineman.
That wasn’t surprising: Thomas set the tone on his first career snap when he had a quarterback pressure that led to an interception.
“It’s early, but the way he played the other night,” Lynch said then, “I had a bunch of people going, ‘Wow.’ And that’s why he was the No. 3 pick in the draft.”
Five months later, after Thomas’ rookie season, some might wonder why, exactly, he was the No. 3 pick.
In 14 games, the Stanford alum had 41 tackles and three sacks and tied for second on the team with 10 tackles for losses. It was a just-OK season that paled in comparison to the previous year’s No. 3 pick: Chargers defensive end Joey Bosa, who was the NFL’s Defensive Rookie of the Year.
Thomas’ first year didn’t result in a similar honor, largely because he didn’t often replicate the pass-rush moment that marked his first game in Kansas City.
Not surprisingly, it’s the area he identified last month when asked about his offseason improvement plan.
“Definitely just being a better pass rusher overall,” Thomas said. “There are a lot of things: work on your bend, violent hands, get-off. So I’m going to focus on all those things this offseason. And they’ll be a big part of what I key in on these next few months.”
Defensive coordinator Robert Saleh said he was happy with Thomas’ first season — highlighting his penetration on run plays — but hit on the same theme.
“There’s the developmental part that we need to get to with regard to consistency in pass rush, which I think he’ll reach,” Saleh said. “I’m not really concerned about it. But as far as his growth, I’m very pleased with where he’s at.”
Thomas vaulted into the draft’s top 10 after creating pass-rush havoc in his final college game: He had five quarterback hurries and a game-sealing sack in the Cardinal’s win over North Carolina in the Sun Bowl 13 months ago.
It didn’t help his pro development that Thomas stayed at Stanford after that game: An NFL rule prohibited him from participating in the 49ers’ offseason program because Stanford, which is on the quarter system, didn’t have graduation ceremonies until mid-June.
His late start put him in catch-up mode and contributed to Thomas feeling pressure to justify his lofty draft selection.
“Definitely at the beginning of the season, of course,” Thomas said. “Then I just calmed down, focused on playing football and having fun. It’s just part of the process of being a rookie: — understanding the pressure and the mental game. I’ve grown a lot, and I’m just going to continue to grow going into my second year.”
In his second season, Thomas probably won’t be asked to serve as a jack-of-all positions.
As a rookie, he played both end spots and usually moved inside in passing situations. The 49ers’ lack of an every-down “Leo,” the end spot reserved for their best pass rusher, meant Thomas moonlighted at the spot.
The 49ers will address their lack of pass rush in the offseason after they tied for 26th in the NFL with 30 sacks. And, if they do so successfully, that figures to allow Thomas to play more inside, where he appears to be best-suited.
In the meantime, he will work to improve after a season that left him acknowledging he’s a work in progress.
“I know it’s going to take time,” Thomas said. “I know it’s not going to happen right away. I know it’s going to be a little bit, but I’m working my butt off. And I’m going to become the player I need to be.”
Eric Branch is a San Francisco Chronicle staff writer. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch