You may be confused as to what a "strike" offense is. Not every felony conviction is a strike; a felony DUI is not a strike unless there are some other factors, such as someone was injured. But if the conviction in would qualify as a "strike" under California law, it can be used as a "strike prior" even though the conviction was from another state. This can become a hotly litigated issue in many cases. Obviously, the best thing to do is to start anew in California and not get in trouble again. Then his priors will not come back to haunt him.