Baby suddenly upset when done a poo

I mean hysterically crying because he’s done a poo, it’s happened twice today and as soon as I change him he’s fine. One was only a very small one too so it’s not like he was proper covered in it 🙈 He is normally very chilled when he does a poo if he’s sitting in it and I can’t change him straight away (car is his favourite place to go). It seems a normal consistency for him and it isn’t very hard so I don’t think he’s constipated. Has this happened to anyone else?