I have two points to make inshaAllah:
1 - People come to Islam in various ways.
Umar ibn Al Khattab accepted Islam after hearing the beautiful message of the Qur'an. Khalid bin Waleed accepted Islam upon the realization that Islam always triumphs and was going to triumph everywhere. رضي الله عنهم And many others accepted Islam because they knew Prophet Muhammad صلى الله عليه وسلم to be upright and truthful.
My point: Every person today is drawn to Islam because of some aspect of it which they liked. Some are drawn to its superior logic, clarity and reason; others are drawn to it because of its beautiful teachings on charity, kindness, etc. Some are drawn to it because of the beautiful life/character of its Messenger, Prophet Muhammad (ﷺ). The list goes on!
The two girls in the video are just telling you what drew them to Islam. And those are valid reasons which they gave too, ie sister #1 loving the Sunnah of the Messenger and sister #2 loving the compassion/brotherhood of the Muslim Ummah (which is the fruit of Islam).
Also, just because a person does not verbally tell you "I'm convinced Islam is the truth" it does not mean that they are not convinced. The fact that they accepted Islam implies that they DO accept it as the truth.. after that initial attraction to it. Unless they say otherwise, then you don't know what's in their heart.. and we always assume the best about fellow Muslims [til they give reason otherwise].
2 - Yes.. people are Muslims if they accept Islam even if they are ignorant about aspects of Islam. You're not required to know everything from the beginning (not even required to know Arabic). You're just required to know what you're saying [Shahadah] and believe in it. However, it's not recommended to dive into it ignorantly. People should study and get a basic understanding of Islam. And thereafter, continue to seek 'ilm (knowledge) which is an Islamic obligation.