Abdel's backstory is far too different from the game protagonist's backstory for anyone to claim that Abdel is the canon identity of the game protagonist.
1. In the first Baldur's Gate game, the narrator says that the game protagonist, who I will refer to as "Gorion's Ward" has been raised in Candlekeep for 20 years of his/her life, meaning he/she was born either in 1346, 1347 or 1348 DR, unlike Abdel, who is confirmed to be born in 1343 DR.
2. According to Throne of Bhaal, Gorion and a group of Harpers rescued Gorion's Ward and Imoen from a temple of Bhaal when they were babies, leaving young Sarevok behind, and Gorion personally knew Gorion's Ward's mother and was a close friend of hers up until she, as a priestess of Bhaal tried to sacrifice her child. As for Abdel, Gorion did not rescue and adopt Abdel. Abdel was saved by a paladin named Sir Daesric from deathstalkers. Sir Daesric was an old friend of Gorion, and he brought Abdel to Gorion. These details come from the letter that reveals to Abdel that he is a Bhaalspawn in the Baldur's Gate novel.
3. Abdel left Candlekeep in 1360 DR to start his career as a mercenary for hire, eight years before the events of Baldur's Gate, while Gorion's Ward has lived in Candlekeep for 20 years up until 1368 DR. The novel constantly claims how well-traveled and experienced Abdel is.
4. The Baldur's Gate games assumes that you are not playing as Abdel, considering that Gorion's Ward's fame and glory do not last in the game. In the games, in the end of Siege of Dragonspear, Gorion's Ward is forced to escape Baldur's Gate due to the authorities of Baldur's Gate not only finding out that he/she is a Bhaalspawn like Sarevok, but also being framed for Skie Silvershield's murder, which Jon Irenicus instigated to lure Gorion's Ward out of Baldur's Gate to capture. Gorion's Ward is even accused for the destruction of Saradush after defeating Yaga Shura. The people of Baldur's Gate would never accept Abdel Adrian as a hero if they believed he did such a thing. In the novelization of Shadows of Amn, Abdel was all in the clear, no one learned he was a Bhaalspawn, and somehow Irenicus managed to capture him without destroying his reputation. Gorion's Ward falls from glory while Abdel is labeled a hero even if he wasn't involved in stopping the iron crisis. It can happen sometimes, a true hero's glory gets stolen by someone else, and history ends up remembering the wrong person as the hero.
5. Viekang never appeared in the Baldur's Gate Trilogy novels, he only appeared in the games. The fact that he appears in the Murder in Baldur's Gate tabletop adventure game to assassinate Abdel means he canonically survived Saradush's destruction in Throne of Bhaal.
6. If the references were directly from the D&D books and campaigns, then characters that never showed up in the novels should not exist like Coran, who also appeared in the Murder in Baldur's Gate campaign adventure. In the Legends of Baldur's Gate comic books, Minsc does not look the way the Shadows of Amn novel described, having red hair and a beard. He knew Neera from the Enhanced Editions of the Baldur's Gate games, and Coran. Minsc knowing Coran is impossible because they never appeared in the first Baldur's Gate book, and Minsc was demoted to merely a side character in the Shadows of Amn novel.