I have a strange feeling that 'fact' is defined differently within the Muslims community. According to the article linked, there 3 main 'facts'.
1. The Muslim worships One God.
2. The effects of Islaamic worship on the soul of the Muslim include the following:
- Prayer keeps the slave in contact with his Lord
- Zakaat purifies the soul from stinginess and miserliness, and accustoms people to being generous and helping the poor and needy
- Fasting involves refraining from food and sex
- Pilgrimage to the sacred House of Allaah
3. Islaam commands all kinds of good and forbids all kinds of evil.
These are facts about Muslims. They do not make Islam any truer than any other religious superstition.
The list of forbidden acts is long and tedious.
The answer to "Why do Muslims think that Islam is true?" is "because Muslims believe in Islam". Get it?