That's because the customized view that you're using hasn't been made to work with anything else than images with the correct ratio as it was done for a very old version of HikaShop and that the code changed since then.
You would need to change the line:
<?php echo $this->image->display($image->file_path,true,$image->file_name,'id="hikashop_main_image" style="margin-top:10px;margin-bottom:10px;display:inline-block;vertical-align:middle"','id="hikashop_main_image_link"'); ?>
to:
<?php
$height = $this->config->get('product_image_y');
$width = $this->config->get('product_image_x');
if(empty($height)) $height=$this->config->get('thumbnail_y');
if(empty($width)) $width=$this->config->get('thumbnail_x');
$divWidth=$width;
$divHeight=$height;
$this->image->checkSize($divWidth,$divHeight,$image);
echo $this->image->display(@$image->file_path,true,@$image->file_name,'id="hikashop_main_image'.$variant_name.'" style="margin-top:10px;margin-bottom:10px;display:inline-block;vertical-align:middle"','id="hikashop_main_image_link"', $width, $height);
?>