There may be cultural differences (esp. regarding the US, which were generally known as somewhat prudish in these concerns), but in Europe sporty swimwear (rather by Adidas and similar domestic brands than real Speedos) was the default. Anything else was asking for an explanation or would even provoke open ridicule (like Hawaiian shorts).

That is almost certainly fair. I know I wore Speedo-like swimwear for water polo but would have worn nylon shorts of some sort at the beach generally.