Welcome to the QIIME2 Forum:qiime2:
Disclaimer: I am not a statistician so I would suggest doing your own research into my answers.
I believe that you can not assume significance.
First, You can’t claim significance from your Ancom results because does not test for significance in its results.
Second, I am assuming that you made this boxplot based on the table that Ancom produces(without more info this is what makes the most sense to me). That Ancom table is absolute counts, not relative frequency. Boxplots based on those absolute counts are not really representative of your data.
Last, this box plot is a great quantitative representation of your data (with the above caveat) but the only way to be able to claim significance is through a qualitative analysis of your data. Statistical tests that give p-values will allow you to make claims of significance but not just looking at a boxplot.
Hope that helps!