Am I overreacting to his coworker being flirty?

We were hanging out and he got a message from a work app (they have to use it because they can’t take their phones in) and he got a message from a girls name I wont mention which he told me is a 37 year old coworker with two kids and a husband. I looked her up on Facebook but I just see kids, no husband. Anyway. She messaged him “heeaaaeeaay” and maybe I’m being too dramatic but to me that’s so weird. Like he says he trained her and then she transferred to a different facility an hour away and that she probably just wants advice or misses coworkers. I’m trying to see that but to me it’s so weird how she sounds flirty by saying that. Idk it doesn’t sound professional at all to me. And I looked her up and she’s cute so that might be why I’m worried. Granted, she likes everything of mine and his on Facebook so she knows about me and he claims she’s texted him about me before just giving him tips on where to take me for dates (he never showed me these messages but he just told me not to worry) and idk he said he wouldn’t message her back and there’s a side of me that doesn’t think he will but there’s still a side of me that thinks he will if he hasn’t already and idk if I just need to stop worrying or if it’s cause for concern. He is also 23, and she really is 37, I just don’t understand why she had to send a message flirty like that. Am I overreacting?