Yep it can REALLY upset some male dogs, and neutered dogs too, not just entire dogs.
Some absolutely lose their minds if there is a bitch in heat anywhere nearby.
Common dog owner courtsey is not to walk in season bitches along busy roads (where the scent may cause a dog otherwise normally reliable off lead, to dash off and cross a road to get to her) and not to walk them off lead or in places people typically walk dogs off lead.
In practice, the first week and last week of the season an anti-mate spray, choosing quiet times of day and on-lead walk routes covers things.
The middle week when the bitch is most fertile, stay home, use hired fields if possible, many bitches won't want to go for long walks anyway, entertain them with training and play at home.
In a perfect world everyone would train their dogs to ignore the scent of a bitch in season - however generally training for a specific thing like that involves having access to that context/trigger to work on the training, and reliably having access to in season bitches to train around is nigh on impossible for the average owner. So its not really a surprise most dogs are not trained to be super reliable around in season bitches.
As for the idea that responsible rescues don't rehome reactive dogs - hilarious. I'd be out of a job if that were true. I have more work than I can handle! Many dogs do not unpack the full 'baggage' of trauma and behavioural issues until they've been in their new home 3+ months, and a home environment is very different to a shelter environment. So its entirely possible the rescue have never seen that behaviour from the dog whilst it was with them, no matter how good they are at behaviour work and assessing dogs.