"search term" can mean a term that is, was, or will be searched. It is like "keyword", which also does not refer to the time of the action (tense).
"searched term" describes a "term" as something that was "searched" (past tense).
In your example, you can use "searched term" to emphasise the past tense. But, as snailplane points out in comments, this is not really necessary, as "search term" can mean "search term that was used" here.
When you need to be clear that the terms were used in the past, for example, in a database that records search terms that were used as opposed to search terms that might be or will be used, then "searched terms" is more concise than "search terms that were used".