Neutered dog has started humping

My 1 year neutered dog has suddenly started humping us. I do divert him with tug play/ puzzle mat. He runs for an hour each morning & evening. This behaviour is very sudden & happening since past 2 days. We got him neutered at 7 months. He doesn’t even understand if given soft toys or pillows for humping purpose. He straight away grabs our arms/legs.
Is this act sexual? And if yes, what should be done?

Humping should not be allowed on soft toys or pillows either. He will hump you if you keep on nurturing the excitement in him.

Instead of running here n there, he needs long structured walks. This is not sexual but he is getting aroused because of too much stimulant and less structured walking.

So start giving him long structured walks.

No we dont encourage soft toys n all… We tell him to stop n he stops for a while but then starts again. Like only once or twice we tried giving a soft toy.
And he goes for walks as well…(not structured may be) . When i take him for walks he tries to humps the female dogs as well… Not the male ones. With male dogs he plays bite bite… But when he finds an indie female, he only goes for humping.