Damn straight it is! A language belongs to everyone and clearly you are proud that you can speak it
May I offer a different perspective to view such bias? Perhaps view your speaking ability as a way to crack other’s bias toward you. Watch their face drop when you speak Cymraeg and demand “Oes ots…” Have a bit of fun with it if you can. This way, if another similar event occurs, your frame of mind will be different. You’ll change yourself and possibly someone else.
I want to share a similar story. My family is from the United States. We are quintessential White America. My incredibly ambitious and successful niece spent several years traveling around Mexico and the Caribbean. Consequently she became fluent in Spanish. She has blond hair, and based upon appearance, and standard American accent she would appear to be one of the last people you would expect to speak Spanish. One day she was helping out at a friend’s construction site that mostly employed Hispanic men. All day they spoke about her the way a group of men would in private (they conversed in Spanish). My niece listened to their comments, not saying a single word. At the end of the day, she walked past them and said with a perfect Spanish accent, “Thank you for the compliments. I appreciated hearing them,” and walked away leaving them stunned and embarrassed. The next day, the Hispanic foreman spoke the to owner, niece’s friend, apologizing profusely because no one expected a blond haired women to speak fluent Spanish. Lessons learned for everyone.