I have never understood this. It works this way for find/found, grind/ground, and others. Why is it not mind/mound?
Find and grind are strong verbs that inherited Proto-Indo-European ablaut. They have been verbs for a very long time.
Mind is a weak verb. The Oxford English Dictionary describes its origin as "Formed within English, by conversion". In other words, the noun mind came first, and the verb mind was derived from the noun. Verbs that are derived from nouns cannot be strong verbs (unless they are altered by analogy). In fact, there is no productive way to derive new strong verbs. They're pretty much all inherited from at least Proto-Germanic verbs (I don't know, there might be a few that come from other sources).
This information is of limited usefulness for determining the conjugation of any particular verb, since often it's hard to tell if an English verb is derived from the corresponding noun, or vice versa (for example, grind and find also exist as nouns, via conversion/zero-derivation from the verbs).