Yes, you have to understand some web technology platforms, especially the most popular web programming languages, and designing tools such as Javascript, HTML, CSS, and PHP if you need to work with the technical SEO side. It is not necessarily required to be a programmer to be an SEO expert, but you have to be able to edit some codes if there are programming issues that are affecting your website ranking. Remember that if you use CMS websites, you will not need coding skills, and it is not often you will find SEO professional writing codes. It happens only in few cases for editing PHP, Javascript, or HTML files.