Its not a risk actually because he is not investing on bitcoin anyway , he only accepts payment via bitcoin which he can adjust the price of the product depending on the price of bitcoin . he wont loose this way and besides , bitcoin is only an alternate option while fiats and other payment method are still available .
Anyways , this is a another good news . thanks to the op because he is helping the bitcoin to spread and become recognizable by others .
It doesn't seem like a risk to me as the percentage of the BTC payments would be tiny compare to traditional payment methods. And again, it's not profit focused action. I just wanna learn about Blockchain by being part of it and I really really want to see some BTC fans buying some coffee with it and have a nice chat about crypto while he/she is sipping his/her drink.