SEO and speaking URLs

I have a question about URLs and whether this could be an SEO problem. For example I have a URL for a product in the shop www.examlpe.com/red-shirt. This URL is in the sitemap. That's fine. But if you search for red socks in the shop via the search gap, you get suggestions with products in a separate window. If you click on the link in this case, you will be redirected to the page www.example.com/1234 instead of www.example.com/red-shirt. The URL www.example.com/1234 is included in robots.txt because we only want the talking URL to be indexed but due to a technical problem the URL is available via the search directly in the shop. So you hava two URLs. And the customer can place an order via both URL. So I wonder if this is a general problem for SEO and why? Thank you !