That is explicitly contradicted by the text of the downloadable encounter's version. First, on page two, it tells you that if you run the game for two hours a week, every week, you will likely finish the first three episodes before the end of the season. Second, after the end of episode three, on the page titled "Additional Play" it explicitly tells you to continue the adventure using the full printed product.
Most telling, to me, is that the store's Encounter's kit contain certificates for the permanent magic items in the full version. In fact, the certificates are only for the full version as there are no magic items in the first three episodes. This is explicitly stated on page 4.
Both of which are also true of Lost Mine of Phandelver.
There is a huge difference between "designed for" and "playable in".
D&D Encounters was originally designed as a 4E program where there would typically be one combat encounter per week. This was largely due to a single combat encounter in D&D 4E taking about an hour, so running a 60-90 minute session each week with one combat rather worked. Every group would do exactly the same encounter each week, no matter where you played.
D&D 5E is a different beast: combats no longer take anywhere that long. As a result, you can do a lot more in a session. Over the past year, Wizards also decided to relax the "every store does the same thing each week". And with Hoard, they've even got the stores starting and ending them at different times!
So, what are the constraints on designing an Encounters adventure these days? Well, no encounter can go over 2 hours in length. That's about it, really. Given that there's pretty much no encounter in all of D&D 5E that is likely to go above 2 hours in length, that's not much of a design constraint.
When you actually read the notes on adapting Hoard to Encounters, it becomes quite clear that the adventure isn't written for Encounters. The way the adaptation works is that each encounter is rated as "short" or "long" and that you should run either one long or two short encounters each session. In the first episode, the DM will likely order the potential missions so that this occurs. What happens in Episode 3, though, which is a dungeon crawl? What happens if the players go from a short encounter to a long one... oh, the DM needs to put in wandering monsters to create another short encounter before they get to the long one, which is then delayed to next session. Which is just a bit clunky.
Hoard isn't designed for Encounters. You have to fiddle with it to make it work.