Basically, when one who is not historically active on LinkedIn suddenly becomes conspicuously so, something is probably happening within their professional life to prompt this. When one is about to change positions, leave a job, or is about to undertake an active job search, they tend to make noticeable changes to their LinkedIn profile. I'm not referring to something innocuous, such as changing their profile picture or altering their headline. What attracts attention is concentrated activity involving: accumulation of network connections, adding multiple professional talents/skills to one's profile, and active solicitation of peer endorsements.
Conspicuous activity in any setting (in the online world as well as the real world) invites attention. In our professional lives, unless we are willing to subject ourselves to speculation regarding our intentions, it is best for us to pursue networking activity on a "slow and steady" basis.