Why does "And this person will claim me on their 2019 tax return" matter if the answer to "Someone else can claim me as a dependent on their tax return" is a Yes.

There is a difference ... just because someone CAN claim you  doesn't mean they WILL claim you. 

If they CAN claim you then you cannot claim yourself PERIOD.   

However, if they do NOT claim you then you are eligible for the non refundable portion of the AOTC ... so the program needs to know both ... CAN you be claimed and WILL you be claimed.  If your AGI is $12K or less then this is really a mute subject. 

If you can be claimed as a dependent under the rules, you must check the box even if the person who could claim you doesn’t want to claim you.

The only tax item that is affected by the second question “will this person actually claim you” is the American opportunity tax credit for college expenses.  In some cases, if your parent could claim you as a dependent but does not, you might be eligible for a portion of that credit. This situation mainly occurs if your parent makes too much money to qualify to include the credit on their tax return.