No, it means just the opposite. It protects the seller from an appraisal below purchase price. Such language is really not needed. When an appraisal comes in low, the seller doesn't HAVE to do anything. The bank may deny the application unless the buyer makes up the difference in cash. It's then up to the buyer to decide if they still want the house anyway, and come up with the extra down payment money. The seller cannot be FORCED to take less. Therefore, language in the contract that 'lets' them out for a low appraisal is unnecessary.
Example: The lender requires a 10% down payment from the buyer. The contract price is $200,000. Down payment is $20,000, the mortgage applied for is $180,000.
But the property appraises for $190k The seller does not have to accept $190k. The lender will only loan 90% of that, or $171k. This means the buyer must come up with the additional $9,000 for down payment. If they can't, and the seller refuses to budge on the price (which they may), the contract is null and void. No language required in the contract to make that the case.
If the appraisal comes in high, the seller may be unhappy, thinking they sold too cheaply. Too bad for them. The bank and the buyer are both very happy. The bank's risk is lower and the buyer thinks they got a great deal.