Stastney expected an aggressive forechecker to back off and defer to his little toe-drag and for Joshua to let him squirm loose rather than get pasted. He paid the price, as he should have. It's hockey, and playoff hockey at that. You need to know how to take a hit from a forechecker on the end boards if you're a defenseman. If that was the best he can do, he'll have a short career. I suspect he'll choose differently next time. Joshua got his penalty - there was nothing particularly malicious in the hit, the guy chose not to protect himself, and he absolutely has an obligation to do so under the circumstances.
The "victim" made an absolutely idiotic play that any hockey player over the age of 12 should know better than to try. You don't turn your back and try to toe drag your way out of an aggressive forecheck on the end boards. What he got comes with the territory. I hope he feels better and can rejoin the series, but get real.