Dating

Date says “wear something nice.” Isn’t this a little rude?

I don’t know him all too well. We’ve only been talking for a few days. We met online. We have a date planned for tomorrow. We were texting about our first date tomorrow and he says “wear something nice”. We are going to the beach to have a picnic. We aren’t going to dinner or lunch, or any restaurants. Why would he say this? It’s not like I’m going to show up in overalls and a straw hat or a bikini. What does he mean by this?
Date says “wear something nice.” Isn’t this a little rude?
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