Depends.
I know you don't like to hear that. So, let's list some of the things that it depends upon.
If his face is neutral or passive, like sheepish or embarassed. Then no, generally.
If his face is aggressive, like angry or judgy, or contemptuous. Then yes.
Lot of times what makes something offensive or not is the look you have on your face.
Was it a single glance, or he was spacing and just settled on her, was he looking to determine something (like how much longer she's in the equipment). Then no.
Is he doing it repeatedly? Was he looking for a really long time? Was he doing so lustfully or predatorily? Then yes.
That's a good primer, I think.
Men this kntbat women don't notice them. This isn't true. We do. We have eyes and have the same societal inclinations to admiring aesthetics as you men do.
So why don't men ever know when they're being admired from afar?
1. You don't notice us to begin with ojtside your own sexual desires.
2. We don't care if you know we're looking like men do. Men want women to know they're being watched. So we're more subtle about it.
3. It's not performative for us. We don't bond with our girlfriends over lusting after some guy like you men do. It's just something we notice and then go about our day. Well, outside Chippendale. Then we act like you men do. 😜 And tip generously. But then, that's what that space is for. And there's consent.
Some women may be reactive about it due to having endured one or more those harassing situations that leave you rattled for a while. It's not personal, just give her space.