The comment was aimed at Bell.
We hear very little from him and this is the tweet we get?
It does not sound filled with bitterness to you?
If he posted on the Steelers all the time, good and bad, sure. I am being unfair.
But that's not the case, is it?
Just like AB and a number of others he made that bed. Now he is bitter toward the Steelers. He needs to look in the mirror.
No, it doesn't sound filled with bitterness, and I can't say Bell's relative quietness regarding the team strikes me as the action of a bitter man either. Not when the last thing I remember about Bell and the Steelers was him saying he'd come out of retirement to play for them and there's been an absolute buffet of possible chances to case shade at the Steelers if one wishes. I mean, who'd opt for the back-up QB doing football in shorts if they really wanted to cast a snook at the team?
Last I heard he accepted he'd made a mistake leaving the Steelers too fwiw.
But even if he was openly bitter as hell and always ragging on the team, I'd still strongly believe in treating his criticisms on the strength of whether they made sense rather than the person who made them.
In this case, he's making a comment that's made by about 19 of the first 20 replies to the tweet. It's a very obvious criticism and honestly, even hearing Fields was working on his progressions doesn't entirely excuse it because some of those waits/out of bounds just look late regardless.
edit: Since I'm easily bored and endlessly curious, I went over Bell's socials for the last 10 days. He celebrates Tomlin's extension calling him the "best in the world" and says they should get Mike Tomlin Jr (Aiyuk). Reposts a couple of gifs of him playing for the Steelers. It doesn't exactly look like bitterness to me.