Answer: Yes, thats possible.
- mail.click without an mail.open can happen if the mail is scanned by a spam/malware system. These System normally generate a click and often multiple as the open each link but mostly also do not generate an open as they do not load the image
- opens are usually tracked by a pixel in the mail content, while clicks are mostly tracked via a redirect over a server. So when a client does not allow images to be loaded for the clients mail or in general, the pixel is not loaded either and we get no mail.open. They can still click though.