That pound or two is probably no more than water retention.
With more carbs eaten, your body restores some of your glycogen stores in your muscles, which otherwise a very low carb diet will keep depleted. Glycogen stores also store water. So the question is really whether the sudden weight gain continues or stabilizes quickly.
Very low carb diets often have a sudden initial weight loss, and that initial weight loss is mostly water loss.
Basically this. Look up ketosis, or "keto" diet.
Glycogen is ready energy stored in your muscles and liver - it's basically a glucose polymer, i.e. carbohydrate, i.e. starch. Glycogen easily releases glucose into the bloodstream from your glycogen stores as you need it.
Some glycogen is stored in the muscles, right where it's needed. Alternately your liver stores enough for a few days use. When the liver is full, excess sugar goes right into fat storage - arbitrated by insulin.
When you deplete your glycogen stores, the body starts producing ketons and using those for energy instead of sugar (i.e. glucose). It makes the ketons from fat - dietary and stored.
Depending on your size there a zone of a few pounds you need to shed to go from a "normal glucose" based metabolism to a "normal keton" based metabolism.
If you are in ketosis and eat a bunch of carbs then some of those carbs are metabolized with the rest going to replenish your glycogen stores (along with plenty of water bound to the glycogen). Your weight will blip up.
As you can see, if you only do a few "low carb" days, followed by "high carb" days, you never really get into ketosis and you weight will easily vary "a lot" as the glycogen stores get worked off or rebuilt. You're just partially depleting your glycogen stores and filling them back up.
To loss weight on keto, you want to get into ketosis and stay there. At least for a while. Getting into ketosis also supresses appetite for many/most people.
It's really more complex than this, but you get the idea (I hope).
Good luck