It doesn't look like he was under the influence at the time, but the term "driving out of his lane" does kind of give reasonable cause for drug use, but maybe thats profiling.
The problem with this logic is that it fails the "prior probability" test.
Suppose a policeman searches and finds the suspect carrying a large amount of cash, say $4000. That's consistent with a (supposed) drug purchase, so the cash can be confiscated under asset forfeiture laws (assets used in the commission of a crime).
Suppose a policeman notes a youtube video of a chemistry experiment showing a balance scale, some beakers, and jars of chemicals. Those are consistent with "meth lab", so the policeman can search and confiscate all the equipment in the poster's house (this has happened).
The problem with each of these, and your position, is that there is significant prior probability that the behaviour in question is *not* indicative of criminal activity. You are reversing the conditional probabilities.
To put it in words, you are equating "probability of driving out-of-lane, given that he's on drugs" (quite high), with "probability that he's using drugs, given out-of-lane driving" (actually, quite low).
People temporarily drive out-of-lane a great deal to avoid animals and small obstacles, and people temporarily drive out-of-lane because they're distracted. The number of people out-of-lane because they're on drugs is vanishingly small.
Taken to extremes (and we know the police will do this), pretty-much *any* behaviour can be considered consistent with drug use.
In the case of the home lab above, it doesn't matter that the poster is missing key components, nor that he only has some of the ingredients. "Meth makers use glassware, he's got glassware, therefore he's a meth maker".
You see where this leads?
If a policeman observes a crime, take the appropriate action - that's fine. If he *observes* another crime while dealing with it, that's fine too.
But that's not a justification to rummage around in a person's rights just to see what can be pinned on the suspect.
If he doesn't observe a crime, he shouldn't go looking for one.