The default avatar there looks like the author email address in those commits is not on your account, so GitHub doesn’t recognize them as yours. There are two options to change that, depending on whether the email address in those commits is correct (as in, yours and able to receive mail):

• If it is correct, you can add the mail address to your account.
• If it is not, you should change your commit email to whichever is the right one. Note that that does not fix past commits. You can rewrite commit history to change that, but read the warning at the top of that article and carefully consider if you really want to do that.