Stating surprise about another researcher in my talk
Talk about the work. Stick to the facts.
Clearly and bluntly stating the limitations of a result is fine, but criticism of a researcher during a research talk is completely inappropriate. Your expression of surprise could be taken as criticism of either the researcher's ethics or their competence, neither of which is appropriate to air in front of a research audience.
Whether the researcher is junior or senior is irrelevant. Whether the researcher is known to your audience or not is irrelevant. Criticism should be delivered privately.
This is fine:
one particular result of mine which shows that a certain method introduced by another researcher several years ago is quite limited.
These are not:
I cannot believe that this researcher did not notice
I cannot imagine that they were not aware
it rather seems that they omitted this limiting result to make their paper seem better.
express my surprise
This is borderline inappropriate:
This limiting result is really simple
In short, show, don't tell. What you express should be backed up by your results. If it's simple, they'll see that by your work, you don't have to say, "This is simple," or "The other researchers should have seen this" - whether they did or did not is irrelevant to your work.
If you happen to have tested for "surprise" or "Other researcher should have known" or "other researcher omitted information" then present the research and let it speak for itself.
You, however, do not need to editorialize on the subject, and certainly shouldn't be adding your own emotional elements or assumptions to your work.
Present your work, and only your work, and back it up with your research results.
When in doubt, stick to discussing the work. Don't try to make any assumptions or claims about what the other researchers did or did not know or do. That way, you can't be accused of trying to go after another researcher, which isn't helpful to anyone, and certainly not young researchers just beginning their careers.