if everyone sold their altcoin to buy back some bitcoin. it is presumed that if they then hoard bitcoin away from exchanges that the 'supply' on the market would diminish and cause high demand on the btc-usd market

for instance back when we had bitcoin price 100x less.. at $350-$700 in 2013-5(now $35k-$70k):
the circulation supply was 13-15mill coins (now 19mill)
the average minnow market order value was 1btc(now 0.01btc)
the average whale market order value was 100btc(now 1btc)

we can see even after 8 years average orders are still only in the same range of $value being invested.

by this i mean the buy orders are still in the same allotment of $400-$700 mninow amounts
people are still investing roughly the same $ per order that they were before.

what has changed is the btc amount per order has decreased to compensate.

EG when someone paid $400 in 2014 they got 1btc. when someone pays $400 now they get 0.01

if we have another btc market supply dip, where the average minnow/whale amount goes to 0.001-0.1 then that will translate to a 1btc being $400k-$700k

..
so with all that said. there is always potential of this happening. but it would require those jumping from altcoin to bitcoin.. to the hoard btc away from markets. instead of using usd-btc markets to exit crypto. after all if they are dropping their alt(for any number of reasons) they may also want to exit bitcoin. thus cause an over supply on the USD-btc market
..
other variable scenarios are.
if people buy bitcoin on the USD-BTC market. then buy their alt on the btc-alt market. .. but do not return to the btc market via the alt. but instead sell their alt straight to alt-usd
EG
     USD
    ↗     ↘
ALT  ←  BTC
this will cause a usd btc price increase and an usd-alt decrease

if however people buy their alt on a use-alt market, and then exit the alt via btc and then to usd
EG
     USD
    ↙     ↖
ALT  →  BTC
this will cause a usd btc price decrease and an usd-alt increase