I am guessing that he is basing this off of what he knows about how McVay feels about Stafford. Then seeing the emphasis made to bolster the interior OL in FA. And then some common sense about the need to keep Stafford healthy & happy so he may plan on playing 2-3 or more years.
So maybe not "inside info", but certainly an inside feel of how McVay thinks and how the Rams have been operating since Staffords tough 22' season.
Since then they used the highest pick that the Rams have had in years, pick 36, and spent it on a OG, then added a 5th rd OT, then trading for & re-signing another OG. Then they brought in another OG this yr in FA.
Now consider that they have a 4th yr decent LT, who will be a FA next yr, and a 33 yr old RT who is only above avg at this point.
When you step back and look at it, if a high ceiling LT prospect is there, it is not a reach to think that they might grab him. Obviously this time they would know to look at character just like they have in recent drafts with their picks, if they go that route.
I will add that the fact that they would still have 3 top 100 picks remaining, that can be spent on defense and or a WR, it makes it even more possible.