It is not likely, but it can happen... Because they can be immature sperm plugs (small ones, not humungous)
Usually you gauge a sexually mature male by the formation of mature sperm plugs and the change in anatomy (the flower bud into the flower at the ends of the hemipenes), but this is not completely accurate.
To be apropos but inappropriate, his balls may have dropped, and he is producing things, he may just be shooting blanks.