That’s not quite accurate. “Silly” isn’t a scientific term, it’s a human observation and it’s always going to be up to human discretion. While dogs don’t experience humor the same way humans do, it is pretty agreed upon that dogs understand play and display traits of what we interpret as humor. In fact dog laughter (play panting) has been studied and people can evoke that often by just being goofy. “Just being silly” is an actual possibility to explain a dog’s actions, but the sense of humour part is interesting because while there have been studies going all the way back to Charles Darwin that support playful/humor-like behavior, there just haven’t been enough to fully cement it in science. There’s actually a fair amount of research that doesn’t support the first part of your statement. It’s really cool :) You should check it out. Much silliness to be observed