From a rational and removed standpoint, it is clearly not acceptable. There are some confounding factors here, however. For one, Google specifically advises to use their hosted version of the font instead of self-hosting. Another issue is that these people are clearly frustrated by the nonchalant attitude of the maintainers when it comes to breaking others work.

If you are telling people to use your hosted version of your open-source contribution yet have no care for responsible stewardship, you are being irresponsible at the expense of others.

If you don’t want emotional responses after purposefully breaking the hard work of many, you are being unreasonable. While we should strive to be respectful and courteous under such tension, I can understand that not everyone is successful every time.

In other words, I think empathy should go both ways here. Usually, I find that others act very unreasonably and rudely towards maintainers of open source contributions. In this case, I think both parties have made mistakes that deserve forgiving (but not ignoring), including the rude emotional reactions. Both parties should apologize to one another.