Let me fix that for you, the overwhelming majority of straight men in medieval/renaissance times in Europe (judging from the ethnicity of the painting and the blue fleur de lis pattern) were agricultural peasants, who dressed in mostly filthy tunics/coifs and if they were lucky, boots, and ate hard bread and vegetables, very rarely meat.
Some of them were a little better off and wore armor.
The 1% ultra wealthy dressed like in the picture. So I'm deducing what this picture calls straight actually means very wealthy. Some of the very wealthy were famously gay too so it doesn't actually make sense.
It comes off as bigoted because the author seems like he really wanted to make a generalization against straight people, when actually, it's a minority of people who have this attitude, certainly not representative of straight sexuality, or even men in general. i guess it isn't bigotry when it's against a non minority group, right op ?
Your own internalized bigotry missed the opportunity to make a good point about not using bigotry to prevent oneself from doing their part for climate change. This us vs them mentality is exactly the reason why climate change is a divisive issue and you're contributing to that divisiveness.