It was a serious claim. He did not say that just because he can barely use Microsoft Office suite and that's all. Well, obviously, he can, very proficiently. In fact, he can do more.
His exposure to computer started since about a decade ago, and expands further after his decision to migrate to Linux and open source software suites. That act of migration does not preclude him to mainstream suites such as Windows and their ecosystem, but it does make him very proficient and versatile in both worlds.
Computer is his playground, and has experiences in various office suites both online and offline, graphic and vector manipulation programs for both vector and raster images, and exposures to various programming and scripting languages. He also has some experiences in managing a web server, can set up SSH servers, and some extensive experiences in working with FTP and Rsync.
He is proficient in the following office suites: Microsoft Offices (Excel, Word, PowerPoint), OpenOffice or LibreOffice (Calc, Writer, Impress), Google Docs, Google Sheets, Google Slides, and Google Forms. His preferred raster and vector image manipulation programs are GIMP and Inkscape. He has prior exposures and some experiences in Bash Scripting, C++, HTML, and CSS.
His understanding of how computer stores information allows him to very efficiently identify what causes a formatting error in a Word document, or even to build up a working lookup table of previous cases and clients in an Excel spreadsheet. At other times, he was asked to clean up a scanned document digitally, and he managed to deliver a crisp and clean image out of a badly lit document photographs.
He is also very proficient in the use of Markdown, and then able to effortlessly convert them to a Microsoft Word document, a PDF, or even a HTML page with Pandoc.
If that is not enough, he also ran and maintain his own website.